234 research outputs found
Machine Learning Algorithms for Provisioning Cloud/Edge Applications
MenciĂłn Internacional en el tĂtulo de doctorReinforcement Learning (RL), in which an agent is trained to make the most
favourable decisions in the long run, is an established technique in artificial intelligence. Its
popularity has increased in the recent past, largely due to the development of deep neural
networks spawning deep reinforcement learning algorithms such as Deep Q-Learning. The
latter have been used to solve previously insurmountable problems, such as playing the
famed game of “Go” that previous algorithms could not. Many such problems suffer the
curse of dimensionality, in which the sheer number of possible states is so overwhelming
that it is impractical to explore every possible option.
While these recent techniques have been successful, they may not be strictly necessary
or practical for some applications such as cloud provisioning. In these situations, the
action space is not as vast and workload data required to train such systems is not
as widely shared, as it is considered commercialy sensitive by the Application Service
Provider (ASP). Given that provisioning decisions evolve over time in sympathy to
incident workloads, they fit into the sequential decision process problem that legacy RL
was designed to solve. However because of the high correlation of time series data, states
are not independent of each other and the legacy Markov Decision Processes (MDPs)
have to be cleverly adapted to create robust provisioning algorithms.
As the first contribution of this thesis, we exploit the knowledge of both the application
and configuration to create an adaptive provisioning system leveraging stationary Markov
distributions. We then develop algorithms that, with neither application nor configuration
knowledge, solve the underlying Markov Decision Process (MDP) to create provisioning
systems. Our Q-Learning algorithms factor in the correlation between states and the
consequent transitions between them to create provisioning systems that do not only
adapt to workloads, but can also exploit similarities between them, thereby reducing
the retraining overhead. Our algorithms also exhibit convergence in fewer learning steps
given that we restructure the state and action spaces to avoid the curse of dimensionality
without the need for the function approximation approach taken by deep Q-Learning
systems.
A crucial use-case of future networks will be the support of low-latency applications
involving highly mobile users. With these in mind, the European Telecommunications Standards Institute (ETSI) has proposed the Multi-access Edge Computing (MEC)
architecture, in which computing capabilities can be located close to the network edge,
where the data is generated. Provisioning for such applications therefore entails migrating
them to the most suitable location on the network edge as the users move. In this thesis,
we also tackle this type of provisioning by considering vehicle platooning or Cooperative
Adaptive Cruise Control (CACC) on the edge. We show that our Q-Learning algorithm
can be adapted to minimize the number of migrations required to effectively run such
an application on MEC hosts, which may also be subject to traffic from other competing
applications.This work has been supported by IMDEA Networks InstitutePrograma de Doctorado en IngenierĂa Telemática por la Universidad Carlos III de MadridPresidente: Antonio Fernández Anta.- Secretario: Diego Perino.- Vocal: Ilenia Tinnirell
MINIMIZATION OF RESOURCE CONSUMPTION THROUGH WORKLOAD CONSOLIDATION IN LARGE-SCALE DISTRIBUTED DATA PLATFORMS
The rapid increase in the data volumes encountered in many application domains has led to widespread adoption of parallel and distributed data management systems like parallel databases and MapReduce-based frameworks (e.g., Hadoop) in recent years. Use of such parallel and distributed frameworks is expected to accelerate in the coming years, putting further strain on already-scarce resources like compute power, network bandwidth, and energy. To reduce total execution times, there is a trend towards increasing execution parallelism by spreading out data across a large number of machines. However, this often increases the total resource consumption, and especially energy consumption, significantly because of process startup costs and other overheads (e.g., communication overheads). In this dissertation, we develop several data management techniques to minimize resource consumption through workload consolidation.
In this dissertation, we introduce a key metric called query span, i.e., number of machines involved in the execution of a query or a job. In order to minimize the per query resource consumption we propose to minimize query span. To that end, we develop several workload-driven data partitioning and replica selection algorithms that attempt to minimize the average query span by exploiting the fact that most distributed environments need to use replication for fault tolerance. Extensive experiments on various datasets show that judicious data placement and replication can dramatically reduce the average query spans resulting in significant reductions in resource consumption. We show our results primarily on two applications, distributed data warehouse system and distributed information retrieval. In the first case, we show that minimizing average query spans can minimize overall resource consumption for a given workload and can also improve the performance of complex analytical queries. In the second case, our approach minimizes the overall search cost as well as effectively trades off search cost with load imbalance.
The best case of resource efficiency for any underlying data processing system is achieved when the job or the query can be run efficiently on a single machine (i.e., query span=1). In the final part of dissertation, we discuss an in-memory MapReduce system optimized for performing complex analytics tasks on input data sizes that fit in a single machine's memory. We argue that systems like Hadoop that are designed to operate across a large number of machines are not optimal in performance for small and medium sized complex analytics tasks because of high startup costs, heavy disk activity, and wasteful checkpointing. We have developed a prototype runtime called HONE that is API compatible with standard (distributed) Hadoop. In other words, we can take existing Hadoop code and run it, without modification, on a multi-core shared memory machine. This allows us to take existing Hadoop algorithms and find the most suitable runtime environment for execution on datasets of varying sizes.
Overall, in this dissertation, our key contributions in this work include identification of key metric query span and its relationship with overall resource consumption in scale-out architectures. We introduce several workload-aware techniques to optimize this key metric. We go on to demonstrate the effectiveness of query span minimization on different application scenarios. In order to take advantage of scale-up architectures effectively we develop novel in-memory MapReduce system HONE for single machine. Our thorough experiments on real and synthetic datasets demonstrate the efficacy of our proposed approaches
Comparative studies of conceptual design and qualification procedures for a Mars probe/lander. Volume V - Subsystem and technical analyses. Book 4 - Instrumentation Final report
Mars probe instrumentation selection, systems interface, and payload definitio
Energy-efficient Communications in Cloud, Mobile Cloud and Fog Computing
This thesis studies the problem of energy efficiency of communications in distributed computing paradigms, including cloud computing, mobile cloud computing and fog/edge computing. Distributed computing paradigms have significantly changed the way of doing business. With cloud computing, companies and end users can access the vast majority services online through a virtualized environment in a pay-as-you-go basis. %Three are the main services typically consumed by cloud users are Infrastructure as a Service (IaaS), Platform as a Service (PaaS) and Software as a Service (SaaS).
Mobile cloud and fog/edge computing are the natural extension of the cloud computing paradigm for mobile and Internet of Things (IoT) devices. Based on offloading, the process of outsourcing computing tasks from mobile devices to the cloud, mobile cloud and fog/edge computing paradigms have become popular techniques to augment the capabilities of the mobile devices and to reduce their battery drain. Being equipped with a number of sensors, the proliferation of mobile and IoT devices has given rise to a new cloud-based paradigm for collecting data, which is called mobile crowdsensing as for proper operation it requires a large number of participants.
A plethora of communication technologies is applicable to distributing computing paradigms. For example, cloud data centers typically implement wired technologies while mobile cloud and fog/edge environments exploit wireless technologies such as 3G/4G, WiFi and Bluetooth. Communication technologies directly impact the performance and the energy drain of the system. This Ph.D. thesis analyzes from a global perspective the efficiency in using energy of communications systems in distributed computing paradigms. In particular, the following contributions are proposed:
- A new framework of performance metrics for communication systems of cloud computing data centers. The proposed framework allows a fine-grain analysis and comparison of communication systems, processes, and protocols, defining their influence on the performance of cloud applications.
- A novel model for the problem of computation offloading, which describes the workflow of mobile applications through a new Directed Acyclic Graph (DAG) technique. This methodology is suitable for IoT devices working in fog computing environments and was used to design an Android application, called TreeGlass, which performs recognition of trees using Google Glass. TreeGlass is evaluated experimentally in different offloading scenarios by measuring battery drain and time of execution as key performance indicators.
- In mobile crowdsensing systems, novel performance metrics and a new framework for data acquisition, which exploits a new policy for user recruitment. Performance of the framework are validated through CrowdSenSim, which is a new simulator designed for mobile crowdsensing activities in large scale urban scenarios
A Pareto-based Metaheuristic for Scheduling HPC Applications on a Geographically Distributed Cloud Federation
International audienceReducing energy consumption is an increasingly important issue in cloud computing, more specif- ically when dealing with High Performance Comput- ing (HPC). Minimizing energy consumption can signif- icantly reduce the amount of energy bills and then in- crease the provider's profit. In addition, the reduction of energy decreases greenhouse gas emissions. Therefore, many researches are carried out to develop new methods in order to make HPC applications consuming less energy. In this paper, we present a multi-objective genetic algorithm (MO-GA) that optimizes the energy consumption, CO2 emissions and the generated profit of a geographically distributed cloud computing infrastructure. We also propose a greedy heuristic that aims to maximize the number of scheduled applications in order to compare it with the MO-GA. The two approaches have been experimented using realistic workload traces from Feitelson's PWA Parallel Workload Archive. The results show that MO-GA outperforms the greedy heuristic by a significant margin in terms of energy consumption and CO2 emissions. In addition, MO-GA is also proved to be slightly better in terms of profit while scheduling more applications
The influence of different surface and heat treatments on the biaxial flexural strength of veneering ceramics for zirconia and strength reliability and mode of fracture of veneering ceramics
Tese de doutoramento, Medicina Dentária (Reabilitação Oral), Universidade de Lisboa, Faculdade de Medicina Dentária, 2011New processing techniques have facilitated the use of Zirconia core materials in all-ceramic dental prostheses. Zirconia has many potential advantages compared to existing core materials; however its performance when layered with veneering ceramics has not been clearly evaluated. Moreover the veneering ceramics used with Zirconia may be ground, polished or glazed during laboratory procedures and/or clinical adjustments. These treatments may affect their strength by introducing microscopic flaws and defects. The purposes of this study were to investigate the effects of surface treatments on the mean biaxial flexural strength of three feldspathic veneering ceramics used to layer Zirconia cores: NobelRondoTM Zirconia veneer ceramic (Nobel BiocareTM AB, Sweden), LavaTM Ceram veneer ceramic (3MTM, ESPETM, Germany), and Vita® VM®9 veneer ceramic (Vita®, Zahnfabrick, Germany) and compare the mean biaxial flexural strength, its reliability, and mode of fracture of bilayered Zirconia discs veneered with the three feldspathic veneering ceramics. For the first part of the study one hundred and eighty monolithic disc specimens (12.7 mm x 2.2mm), sixty for each feldspathic veneering ceramic were prepared according to the manufacturer’s instruction and divided into eighteen groups, 6 groups for each feldspathic veneering ceramic with 10 specimens for each group. The six groups for each feldspathic veneering ceramic were untreated, grounded, grounded and polished, grounded and glazed, grounded polished and glazed and polished and glazed. Mean biaxial flexural strength and Weibull modulus were appraised. Statistical significance Summary 236 among groups of population was analyzed using one-way and two-way ANOVA and Fisher's PLSD comparison tests. For the second part of the study sixty bilayered disc specimens (12.7 mm x 2.2 mm), twenty for each feldspathic veneering ceramic were prepared using sixty Zirconia core discs (12.7 mm x 1.1 mm) layered with the three feldspathic veneering ceramics according to the manufacturer’s instruction and divided into 6 groups of 10 specimens for each material. Mean biaxial flexural strength and Weibull modulus were appraised, and a scanning electron microscope was used to describe surface features. Statistical significance among groups of population was analyzed using two-way ANOVA, Fisher's PLSD and Student’s t-test comparison tests. For the first part of the study and when the veneering ceramics were analyzed together the data provided strong evidence that there was a significant difference in biaxial flexural strength between the grinding groups and all other groups. When the feldspathic veneering ceramics were analyzed individually data revealed more heterogeneity between the mean biaxial strength of different groups. However, grinding decrease the strength of veneering ceramics and in some cases significantly. For this reason, grinding should always be avoided if any other procedure is to be done, as this will either create or change the developed crack dimensions or increase the volume loss. Conversely polishing and glazing improved the strength of all materials and in same cases significantly. These procedures are recommended to counteract the detrimental effects of grinding which was related to the ability of the procedures to improve the condition of the ceramic’s surface and free it from various defects and flaws. The Weibull modulus values for the veneering ceramics tested varied with different treatments. They showed higher values for polished, glazed and untreated groups, and lower values for ground groups. For the bilayered specimens when the veneering ceramics were Summary 237 analyzed together, specimens with the core material on the bottom surface were statistically stronger and more reliable than those with the veneering ceramics on the bottom surface. When analyzed individually only in the NobelRondoTM Zirconia veneer ceramic there was no significant difference when the core material or the veneering ceramic was on the bottom surface. Two different modes of fracture were observed in the bilayered specimens according to which material was on the bottom surface. The material that underwent tensile stress dictated the strength, reliability, and fracture mode of the specimens. The design of the restorations and the actual distribution of the tensile stresses must be taken into account, otherwise the significant contribution of stronger and tougher core materials to the performance of all-ceramic Zirconia-based restorations may be offset by the weaker veneering ceramics.Com o objectivo de ultrapassar as limitações dos materiais em cerâmica pura tradicionais, diversas companhias introduziram em medicina dentária reabilitadora um material de elevada resistĂŞncia composto por cerâmica de ZircĂłnia. A sua aplicação em prostodontia está a emergir devido fundamentalmente Ă s suas excelentes propriedades mecânicas, biolĂłgicas e estĂ©ticas e ao desenvolvimento de novas tecnologias, como a tecnologia CAD/CAM, que permitem a confecção de coroas unitárias e prĂłteses parciais fixas de uma forma standardizada e eficiente. Apesar das enormes e aparentes vantagens da ZircĂłnia, comparativamente aos materiais cerâmicos tradicionais utilizados como infraestrutura de restaurações protĂ©ticas, o seu desempenho clĂnico quando estratificada com cerâmicas feldspáticas de revestimento nĂŁo tem sido atĂ© agora avaliada com evidĂŞncia. Do ponto de vista da selecção de material, a substituição de materiais cerâmicos tradicionais ou mesmo alumina por ZircĂłnia com maior resistĂŞncia deveria melhorar a performance clĂnica das coroas tendo como referĂŞncia a origem da fractura. No entanto, a resistĂŞncia das cerâmicas feldspáticas, e consequentemente de uma restauração em cerâmica pura com nĂşcleo de ZircĂłnia, está dependente do grau de polimento final da restauração e dos diferentes procedimentos de fabricação no laboratĂłrio e ou ajustes clĂnicos que possibilitem uma correcta adaptação e ou oclusĂŁo. Os procedimentos de processamento e ou ajustes clĂnicos sĂŁo passĂveis de provocar pequenos defeitos microcĂłpicos e ou fissuras sub-crĂticas, que poderĂŁo ser Resumo 240 acompanhados por uma alteração e consequente redução de resistĂŞncia Ă fractura. A presença destas fissuras pode como consequĂŞncia de carga clĂnica e ou presença de humidade crescer para uma situação crĂtica limite levando a falha catastrĂłfica. O efeito dos procedimentos de processamento de materiais cerâmicos tem sido estudado por numerosos investigadores. No entanto, existe ainda controvĂ©rsia no que respeita ao melhor mĂ©todo para produzir a superfĂcie mais polida e resistente. No sentido de avaliar todas estas suposições os objectivos deste estudo foram avaliar a resistĂŞncia Ă fractura medida atravĂ©s da resistĂŞncia Ă flexĂŁo biaxial de cerâmicas feldspáticas de revestimento de ZircĂłnia quando submetidas a tratamentos de superfĂcie nomeadamente, desgaste, polimento e tratamento tĂ©rmico; e avaliar a resistĂŞncia, a fiabilidade e o modo de fractura de restaurações em cerâmica pura com infra-estrutura de ZircĂłnia estratificadas com diferentes cerâmicas de revestimento. Para alcançar estes objectivos, foram efectuadas avaliações quantitativas da resistĂŞncia Ă flexĂŁo biaxial, avaliações qualitativas da ultramorfologia e modo de fractura da interface cerâmica de revestimento – infraestrutura de ZircĂłnia. A estratĂ©gia seguida levou Ă formulação das seguintes hipĂłteses experimentais: H1.0: NĂŁo existem diferenças significativas na resistĂŞncia Ă fractura, medida em termos de resistĂŞncia Ă flexĂŁo biaxial, entre os diferentes tratamentos de superfĂcie no conjunto das cerâmicas feldspáticas de revestimento. H1.1: Existem diferenças significativas na resistĂŞncia Ă fractura, medida em termos de resistĂŞncia Ă flexĂŁo biaxial, entre os diferentes tratamentos de superfĂcie no conjunto das cerâmicas feldspáticas de revestimento. Resumo 241 H2.0: NĂŁo existem diferenças significativas na resistĂŞncia Ă fractura, medida em termos de resistĂŞncia Ă flexĂŁo biaxial, entre os diferentes tratamentos de superfĂcie em cada uma das cerâmicas feldspáticas de revestimento. H2.1: Existem diferenças significativas na resistĂŞncia Ă fractura, medida em termos de resistĂŞncia Ă flexĂŁo biaxial, entre os diferentes tratamentos de superfĂcie em cada uma das cerâmicas feldspáticas de revestimento. H3.0: NĂŁo existem diferenças significativas na resistĂŞncia Ă fractura, medida em termos de resistĂŞncia Ă flexĂŁo biaxial, no conjunto das cerâmicas feldspáticas de revestimento/infra-estruturas de ZircĂłnia independentemente do material submetido a stress tensional. H3.1: Existem diferenças significativas na resistĂŞncia Ă fractura, medida em termos de resistĂŞncia Ă flexĂŁo biaxial, no conjunto das cerâmicas feldspáticas de revestimento/infra-estruturas de ZircĂłnia independentemente do material submetido a stress tensional. H4.0: NĂŁo existem diferenças significativas na resistĂŞncia Ă fractura, medida em termos de resistĂŞncia Ă flexĂŁo biaxial, em cada uma das cerâmicas feldspáticas de revestimento/infra-estruturas de ZircĂłnia independentemente do material submetido a stress tensional. H4.1: Existem diferenças significativas na resistĂŞncia Ă fractura, medida em termos de resistĂŞncia Ă flexĂŁo biaxial, em cada uma das cerâmicas feldspáticas de revestimento/infra-estruturas de ZircĂłnia independentemente do material submetido a stress tensional. H5.0: NĂŁo existem diferenças significativas no modo de fractura das cerâmicas feldspáticas de revestimento/infra-estruturas de ZircĂłnia Resumo 242 independentemente do material submetido a stress tensional. H5.1: Existem diferenças significativas no modo de fractura das cerâmicas feldspáticas de revestimento/infra-estruturas de ZircĂłnia independentemente do material submetido a stress tensional. Na primeira parte da investigação uma amostra de conveniĂŞncia de cento e oitenta (180) espĂ©cimes em forma de disco (12.7 mm x 2.2 mm) foram preparados e usados neste estudo. Os discos foram fabricados com cerâmica feldspática utilizada para estratificar infra-estruturas de ZircĂłnia 3YTZP de trĂŞs (3) marcas comerciais: NobelRondoTM Zirconia veneer ceramic (Nobel BiocareTM AB, SuĂ©cia), LavaTM Ceram veneer ceramic (3MTM, ESPETM, Alemanha), e Vita® VM®9 veneer ceramic (Vita®, Zahnfabrick, Alemanha). Sessenta (60) espĂ©cimes monolĂticos de cada cerâmica foram fabricadas de acordo com as instruções ISO/DIS 6872: 1995 (three-point and biaxial flexural strength) usando um molde de aço inoxidável (ISO/DIS 6872: 1995). O lĂquido de mistura e o pĂł cerâmico foram combinados nas proporções recomendadas pelo fabricante. A mistura resultante de cerâmica feldspática foi vibrada e compactada no molde e posteriormente sinterizada em forno especĂfico para cerâmica (Programat P500, Ivoclar Vivadent AG, Liechtenstein). ApĂłs a primeira sinterização mais cerâmica foi adicionada por forma a compensar a contracção resultante da primeira sinterização. Os discos de cerâmica produzidos foram examinados com um estereomicroscĂłpio (Nikon SMZ-U, Tokyo, Japan) com uma ampliação X75 para avaliar a presença de pequenas fissuras ou poros. EspĂ©cimes que demonstrassem defeitos visĂveis foram substituĂdos. A superficie de todas os espĂ©cimes foi posteriormente polida com discos de carbureto de silĂcio (grĂŁo P220, P500, P1200 - Ultra-Prep, Buehler Ltd., Lake Bluff, IL, EUA) numa lixadora mecânica (Ecomet® 3, Buehler Ltd., Lake Buff, IL, EUA) de acordo Resumo 243 com ISO 6344-1: 1998 (ISO/DIS 6344-1: 1998). Este procedimento foi efectuado atĂ© serem obtidos espĂ©cimes com 2.2(± 0.1) mm por 12.7(± 0.1) mm de espessura e diâmetro respectivamente. Um transportador especial de aço inoxidável foi utilizado para assegurar a uniformização da espessura e paralelismo das superficies durante o corte e polimento. As dimensões dos espĂ©cimes foram avaliadas atravĂ©s da utilização de um medidor digital (Digimatic Caliper Series 500, Mitutoyo America Corporation, Aurora, IL, EUA) por forma a garantir espessura e diâmetros exactos. Finalmente, todas os espĂ©cimes foram limpas com água destilada num banho de ultra-sons (Eurosonic® 4D, Euronda, Vicenza, Italia) durante 15 minutos e posteriormente colocados no forno especĂfico para cerâmica onde foram auto-glazeados. ApĂłs o glaze, a espessura final e o diâmetro foram novamente avaliados atravĂ©s da utilização do mesmo medidor digital atĂ© ao centĂ©simo de milimetro. Os cento e oitenta (180) espĂ©cimes foram aleatoriamente distribuidos por dezoito grupos, seis grupos para cada cerâmica, cada grupo composto por dez espĂ©cimes. Os seis grupos experimentais de cada cerâmica foram fabricados como anteriormente descrito e submetidos aos seguintes tratamentos de superfĂcie: 1) preparação segundo as instruções do fabricante (grupo de controlo) (C), 2) com desgaste/corte da superfĂcie com instrumento de diamante (G), 3) com desgaste/corte da superfĂcie com instrumento de diamante seguido de glaze (GG), 4) com desgaste/corte da superfĂcie com instrumento de diamante seguido de polimento (GP), 5) com desgaste/corte da superfĂcie com instrumento de diamante seguido de polimento e glaze (GPG), 6) Com polimento da superfĂcie seguido de glaze (PG). A resistĂŞncia máxima Ă fractura foi medida atravĂ©s do mĂ©todo “pistonon- three-ball” utilizando uma máquina de testes mecânicos universal Instron (Modelo TT-BM Instron Corp., Canton, MA), e de acordo com o standard ISO/DIS 6872 para cerâmicas dentárias (ISO/DIS 6872: 1995). A resistĂŞncia Resumo 244 máxima Ă fractura (N) foi registada e conjugada com a seguinte formula (ASTM F 394-78, 1996), por forma a obter e calcular a resistĂŞncia Ă flexĂŁo biaxial para cada espĂ©cime: S = - 0.2387 P(X – Y)/d2 (ISO/DIS 6872: 1995). Conjuntamente foi calculado o Weibull modulus para a resistĂŞncia Ă flexĂŁo biaxial obtida. A análise estatĂstica dos resultados foi efectuada atravĂ©s da utilização do mĂ©todo one-way and two-way ANOVA com ajustamento de Fisher's PLSD post-hoc para comparações mĂşltiplas (p=0.05), para avaliar as diferenças de resistĂŞncia Ă fractura entre grupos. Na segunda parte da investigação uma amostra de coveniĂŞncia de sessenta (60) espĂ©cimes em forma de disco (12.7 mm x 2.2 mm) foram preparados e usados neste estudo. Os discos foram fabricados utilizando sessenta discos de ZircĂłnia 3Y-TZP produzidos por CAD/CAM (Nobel BiocareTM AB, SuĂ©cia) (12.7 mm x 1.1 mm) que foram revestidos com cerâmica feldspática utilizada para estratificar infra-estruturas de ZircĂłnia 3YTZP de trĂŞs (3) marcas comerciais: NobelRondoTM Zirconia veneer ceramic (Nobel BiocareTM AB, SuĂ©cia), LavaTM Ceram veneer ceramic (3MTM, ESPETM, Alemanha), e Vita® VM®9 veneer ceramic (Vita®, Zahnfabrick, Alemanha). A preparação dos sessenta (60) espĂ©cimes, vinte (20) de cada cerâmica foi efectuada de acordo com as instruções ISO/DIS 6872: 1995 (three-point and biaxial flexural strength) (ISO/DIS 6872: 1995) usando as recomendações especĂficas de cada fabricante e de acordo com o procedimento efectado para os espĂ©cimes monolĂticos de cada cerâmica. Os sessenta (60) espĂ©cimes foram aleatoriamente distribuidos por seis grupos, dois grupos para cada cerâmica, cada grupo composto por dez espĂ©cimes. A resistĂŞnicia máxima Ă fractura foi medida atravĂ©s do mĂ©todo pistonon- three-ball utilizando uma máquina de testes mecânicos universal Instron Resumo 245 (Modelo TT-BM Instron Corp., Canton, MA), e de acordo com o standard ISO/DIS 6872 para cerâmicas dentárias (ISO/DIS 6872: 1995). Em trinta (30) espĂ©cimes, dez por cerâmica, a força foi aplicada na cerâmica felsdpática de revestimento. Nos restante trinta (30), dez por cerâmica, a força foi aplicada na infra-estrutura de ZircĂłnia. O objectivo de inverter a posição dos espĂ©cimes foi perceber a influĂŞncia que a cerâmica de revestimento teria na origem interna ou externa da fractura do material. A máxima resistĂŞncia Ă fractura (N) foi registada e conjugada com a seguinte formula (ASTM F 394- 78, 1996), por forma a obter e calcular a resistĂŞncia Ă flexĂŁo biaxial para cada especime: S = - 0.2387 P(X – Y)/d2 (ISO/DIS 6872: 1995). Conjuntamente foi calculado o Weibull modulus para a resistĂŞncia Ă flexĂŁo biaxial obtida. A análise estatĂstica dos resultados foi efectuada atravĂ©s da utilização do mĂ©todo two-way ANOVA com ajustamento de Fisher's PLSD post-hoc e Student’s t-test para comparações mĂşltiplas (p=0.05), para avaliar as diferenças de resistĂŞncia Ă fractura entre grupos. ApĂłs os testes de fractura todos os espĂ©cimes foram analisados com um estereomicrocĂłpio (Nikon SMZ-U, Tokyo, Japan) com uma ampliação de X75 no sentido de caracterizar a origem e modo de fractura. A caracterização morfolĂłgica dos diferentes tipos de fractura registados na interface ZircĂłnia/cerâmica feldspática de revestimento foi efectuada atravĂ©s da utilização de microcopia electrĂłnica de varrimento (SEM) (Amray 1820, Bedford, MA, USA). Seis espĂ©cimes representativos, dois de cada grupo, foram seleccionados e fotografias de diferentes amplitudes foram efectudas. Os resultados para a primeira parte do estudo demonstraram que quando as cerâmicas feldspáticas de revestimento sĂŁo analizadas em conjunto, os grupos de desgaste (G) apresentarm diferenças significativas em relação a todos os outros grupos. Foram encontradas tambĂ©m diferenças significativas entre os grupos de controlo (C) e os grupos de polimento/glaze (PG). Nenhuma outra diferença significativa de resistĂŞncia Ă flexĂŁo biaxial, Resumo 246 entre os restantes grupos de tratamento de superfĂcie foi encontrada. Quando as cerâmicas feldspáticas de revestimento foram analizadas individualmente, os resultados encontrados da resistĂŞncia Ă flexĂŁo biaxial entre os diferentes grupos de tratamento de superfĂcie, foram mais heterogĂ©neos. No entanto, em todos as cerâmicas o tratamento de superfĂcie de degaste/corte (G) provocou uma diminuição de resistĂŞncia Ă flexĂŁo biaxial, e em alguns casos de forma estatisticamente significativa. Estes resultados sugerem que o desgaste da superfĂcie destas cerâmicas deve ser sempre evitado se nenhum outro tratamento de superfĂcie for efectuado posteriormente, uma vez que o desgaste ou corte com instrumento de diamante poderá criar ou alterar as dimensões de fissuras ou poros prĂ©existententes diminuindo a resistĂŞncia do material. Pelo contrário, os resultados da resistĂŞncia Ă flexĂŁo biaxial para os tratamentos de superficie de polimento e/ou glaze (GG, GP, GPG, PG) melhoraram a resistĂŞncia Ă flexĂŁo biaxial dos materiais cerâmicos, e em alguns casos de forma estatisticamente significativa. Os resultados sugerem que estes tratamentos de superfĂcie limitam os efeitos do desgaste/corte, devido Ă sua capacidade para melhorar as condições da superfĂcie da cerâmica, atravĂ©s da eliminação ou diminuição de defeitos, fissura e/ou poros. Os resultados sugerem que as diferenças de distribuição da resistĂŞncia Ă flexĂŁo biaxial entre os diferentes grupos de tratamento de superfĂcie estĂŁo mais dependentes da rugosidade de superfĂcie de cada cerâmica e consequentemente do tratamento de superfĂcie efectuado, do que com a sua estrutura; excepto quando a estrutura interna do material possa provocar uma concentração de stress superior aquela originada pela rugosidade de superfĂcie e/ou a presença de poros ou fissuras. Os resultados encontrados demonstraram tambĂ©m, que os valores obtidos para as cerâmicas feldspáticas de revestimento para ZircĂłnia (grupo de controlo), se encontram dentro dos valores que as cerâmicas feldspáticas Resumo 247 de revestimento nos sistemas metálicos apresentam. Os resultados encontrados para o Weibull modulus das trĂŞs cerâmicas testadas sĂŁo semelhantes aos valores obtidos para outras cerâmicas feldspáticas de revestimento. Valores mais elevados foram encontrados para os grupos de polimento, glaze e de controlo, demonstrando maior homogeneidade de valores obtidos, do que para os grupos de desgaste. Os resultados para a segunda parte do estudo demonstraram que, quando os valores da resistĂŞncia Ă flexĂŁo biaxial das cerâmicas feldspáticas de revestimento/infra-estrutura ZircĂłnia sĂŁo analizadas em conjunto, os espĂ©cimes que foram testados com a infra-estrutura de ZircĂłnia na superfĂcie inferior, apresentaram valores estatisticamente superiores aqueles que apresentaram as cerâmicas feldspáticas de revestimento sob tensĂŁo. Quando analizadas individualmente apenas a NobelRondoTM Zirconia veneer ceramic nĂŁo demonstrou diferenças significativas independentemente do material que era colocado sob tensĂŁo. Estes resultados demonstram, que o contributo de infra-estruturas mais resistentes no desempenho clĂnico de restaurações em cerâmica pura, poderá nĂŁo ser significativo se o desenho da restauração nĂŁo tiver em atenção a distribuição do stress tensional sobre ela exercido. Os resultados encontrados para o Weibull modulus das trĂŞs cerâmicas testadas sĂŁo semelhantes aos valores obtidos para outras cerâmicas feldspáticas de revestimento quando estratificadas sobre infra-estruturas diferentes da ZircĂłnia. Valores mais elevados foram encontrados para os grupos que apresentavam a ZircĂłnia sob tensĂŁo, evidenciando maior homogeneidade de valores obtidos. Dois modos de fractura diferentes foram predominantemente encontrados nos espĂ©cimes, dependendo do material que era colocado em tensĂŁo. Quando a ZircĂłnia era colocada em tensĂŁo, um cone Hertziano estava presente na superfĂcie da cerâmica feldspática em practicamente todos os espĂ©cimes. A presença deste cone, era acompanhado por traços de Resumo 248 fractura que se propagavam lateralmente causando eventual delaminação parcial da cerâmica feldspática de revestimento sem fractura da infraestrutura de ZircĂłnia. Pelo contrário, quando as cerâmicas de revestimento eram colocadas sob tensĂŁo, a fractura
Secure Communication in Disaster Scenarios
Während Naturkatastrophen oder terroristischer Anschläge ist die bestehende Kommunikationsinfrastruktur häufig überlastet oder fällt komplett aus. In diesen Situationen können mobile Geräte mithilfe von drahtloser ad-hoc- und unterbrechungstoleranter Vernetzung miteinander verbunden werden, um ein Notfall-Kommunikationssystem für Zivilisten und Rettungsdienste einzurichten. Falls verfügbar, kann eine Verbindung zu Cloud-Diensten im Internet eine wertvolle Hilfe im Krisen- und Katastrophenmanagement sein.
Solche Kommunikationssysteme bergen jedoch ernsthafte Sicherheitsrisiken, da Angreifer versuchen könnten, vertrauliche Daten zu stehlen, gefälschte Benachrichtigungen von Notfalldiensten einzuspeisen oder Denial-of-Service (DoS) Angriffe durchzuführen. Diese Dissertation schlägt neue Ansätze zur Kommunikation in Notfallnetzen von mobilen Geräten vor, die von der Kommunikation zwischen Mobilfunkgeräten bis zu Cloud-Diensten auf Servern im Internet reichen. Durch die Nutzung dieser Ansätze werden die Sicherheit der Geräte-zu-Geräte-Kommunikation, die Sicherheit von Notfall-Apps auf mobilen Geräten und die Sicherheit von Server-Systemen für Cloud-Dienste verbessert
Modelling, Dimensioning and Optimization of 5G Communication Networks, Resources and Services
This reprint aims to collect state-of-the-art research contributions that address challenges in the emerging 5G networks design, dimensioning and optimization. Designing, dimensioning and optimization of communication networks resources and services have been an inseparable part of telecom network development. The latter must convey a large volume of traffic, providing service to traffic streams with highly differentiated requirements in terms of bit-rate and service time, required quality of service and quality of experience parameters. Such a communication infrastructure presents many important challenges, such as the study of necessary multi-layer cooperation, new protocols, performance evaluation of different network parts, low layer network design, network management and security issues, and new technologies in general, which will be discussed in this book
Sustainable scheduling policies for radio access networks based on LTE technology
A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements for the degree of Doctor of PhilosophyIn the LTE access networks, the Radio Resource Management (RRM) is one of the most important modules which is responsible for handling the overall management of radio resources. The packet scheduler is a particular sub-module which assigns the existing radio resources to each user in order to deliver the requested services in the most efficient manner. Data packets are scheduled dynamically at every Transmission Time Interval (TTI), a time window used to take the user’s requests and to respond them accordingly. The scheduling procedure is conducted by using scheduling rules which select different users to be scheduled at each TTI based on some priority metrics. Various scheduling rules exist and they behave differently by balancing the scheduler performance in the direction imposed by one of the following objectives: increasing the system throughput, maintaining the user fairness, respecting the Guaranteed Bit Rate (GBR), Head of Line (HoL) packet delay, packet loss rate and queue stability requirements. Most of the static scheduling rules follow the sequential multi-objective optimization in the sense that when the first targeted objective is satisfied, then other objectives can be prioritized. When the targeted scheduling objective(s) can be satisfied at each TTI, the LTE scheduler is considered to be optimal or feasible. So, the scheduling performance depends on the exploited rule being focused on particular objectives. This study aims to increase the percentage of feasible TTIs for a given downlink transmission by applying a mixture of scheduling rules instead of using one discipline adopted across the entire scheduling session. Two types of optimization problems are proposed in this sense: Dynamic Scheduling Rule based Sequential Multi-Objective Optimization (DSR-SMOO) when the applied scheduling rules address the same objective and Dynamic Scheduling Rule based Concurrent Multi-Objective Optimization (DSR-CMOO) if the pool of rules addresses different scheduling objectives. The best way of solving such complex optimization problems is to adapt and to refine scheduling policies which are able to call different rules at each TTI based on the best matching scheduler conditions (states). The idea is to develop a set of non-linear functions which maps the scheduler state at each TTI in optimal distribution probabilities of selecting the best scheduling rule. Due to the multi-dimensional and continuous characteristics of the scheduler state space, the scheduling functions should be approximated. Moreover, the function approximations are learned through the interaction with the RRM environment. The Reinforcement Learning (RL) algorithms are used in this sense in order to evaluate and to refine the scheduling policies for the considered DSR-SMOO/CMOO optimization problems. The neural networks are used to train the non-linear mapping functions based on the interaction among the intelligent controller, the LTE packet scheduler and the RRM environment. In order to enhance the convergence in the feasible state and to reduce the scheduler state space dimension, meta-heuristic approaches are used for the channel statement aggregation. Simulation results show that the proposed aggregation scheme is able to outperform other heuristic methods. When the aggregation scheme of the channel statements is exploited, the proposed DSR-SMOO/CMOO problems focusing on different objectives which are solved by using various RL approaches are able to: increase the mean percentage of feasible TTIs, minimize the number of TTIs when the RL approaches punish the actions taken TTI-by-TTI, and minimize the variation of the performance indicators when different simulations are launched in parallel. This way, the obtained scheduling policies being focused on the multi-objective criteria are sustainable. Keywords: LTE, packet scheduling, scheduling rules, multi-objective optimization, reinforcement learning, channel, aggregation, scheduling policies, sustainable
- …